A particle beam or radiation projection screen generally has a mask permeable to the image forming medium, i.e. a high-energy beam, at least at one point and has a thermal expansion coefficient which is different from the thermal expansion coefficient of a retaining frame so that by a temperature change the mask foil is put under tension so that the foil is in a planar state.
It is already known to provide a metallic mask foil in the tubular glass body of a cathode ray tube (British Patent 1 163 495).
Since glass has a coefficient of thermal expansion which is less than that of a metal, tension--in as much as the mask foil is anchored in the heated state in the glass material--is produced in the mask foil when it cools down.
The anchoring must according to British Patent 1 163 495 occur at a higher temperature than the crystallization point in order to melt the glass body. On subsequent cooling to room temperature the metal mask foil is put under a considerable tension to the point that the elastic limit of the foil material can be exceeded so that plastic changes occur in the mask foil.